The present invention relates to methods and apparatus for sputtering ionized material from a solid target, or cathode, onto a workpiece or etching a workpiece with the aid of an inductively coupled plasma.
In the performance of a variety of semiconductor device fabrication procedures, ions are directed against a workpiece, such as a semiconductor wafer, or a group of semiconductor wafers. Such an operation involves creation of a plasma in a processing chamber, the plasma being created by establishing an RF field within the processing chamber, while the chamber contains a gas which is ionized by the field. In the case of an inductively coupled plasma generator, the field is produced by a coil.
In one process, a target body is also disposed in the chamber and is electrically biased to a potential that will attract ions to the target. Bombardment of the target with ions causes atoms of the target material to be ejected from the surface thereof. This action, known as "sputtering", is conventionally aided by associating the target with a magnet assembly, or magnetron, which produces a magnetic field that facilitates the creation of ions in the vicinity of the target.
Atoms ejected from the target may be ionized in the plasma and the substrate may be biased to a potential that will attract the target material ions. Typically, the target material is a metal, such as titanium or aluminum. Because the ions to be attracted to the substrate are usually positively charged, the substrate is, therefore, typically negatively biased.
The coil employed to produce the inductively coupled plasma acts as the primary winding of a transformer, with the plasma acting as a single turn secondary winding of the transformer.
Sputtering apparatus typically have a shield to protect the interior walls of the chamber from the sputtered material. As set forth in greater detail in copending application Ser. No. 08/559,345, filed Nov. 15, 1995, allowed entitled "Method and Apparatus for Generating a Plasma" and assigned to the assignee of the present application, the plasma generating coil of apparatus of this type can be installed within the shield of the processing chamber or mounted outside of the chamber shield. In either form of construction, the coil can have a single turn or a plurality of turns.
When the plasma generating coil is installed within the processing chamber shield, as set forth in codending application Ser. No. 08/680,335, filed Jul. 10, 1996, now abandoned entitled "Coils for Generating a Plasma and for Sputtering" and assigned to the assignee of the present application, the coil can be made of a material which permits the coil to provide an auxiliary sputtering source. In addition, as set forth in copending application Ser. No. 08/857,921, filed May 16, 1997 allowed entitled "Use of Variable Impedance to Control Coil Sputter Distribution" and assigned to the assignee of the present application, it has been found that both the rate at which material is sputtered from such a coil and the RF voltage distribution around the coil can vary as a function of coil location about the center axis of the processing chamber. These variances can contribute to nonuniformities in the processing of workpieces.